Heretofore in wide use as motor vehicle air conditioner evaporators are those of the so-called stacked plate type which comprise a plurality of flat hollow bodies arranged in parallel and each composed of a pair of dishlike plates facing toward each other and brazed to each other along peripheral edges thereof, and a louvered corrugated fin disposed between and brazed to each adjacent pair of flat hollow bodies. In recent years, however, it has been demanded to provide evaporators further reduced in size and weight and exhibiting higher performance.
To meet such a demand, the present applicant has already proposed an evaporator which comprise a heat exchange core composed of tube groups in the form of two rows arranged in parallel in the front-rear direction and each comprising a plurality of heat exchange tubes arranged at a spacing, a refrigerant inlet-outlet header tank disposed at the upper end of the heat exchange core and a refrigerant turn header tank disposed at the lower end of the heat exchange core, the refrigerant inlet-outlet header tank having its interior divided by a partition into a refrigerant inlet header positioned on the front side and a refrigerant outlet header positioned on the rear side, the inlet header being provided with a refrigerant inlet at one end thereof, the outlet header being provided with a refrigerant outlet at one end thereof alongside the inlet, the refrigerant turn header tank having its interior divided by a partition wall into a refrigerant inflow header positioned on the front side and a refrigerant outflow header positioned on the rear side, the partition wall of the refrigerant turn header tank having a plurality of refrigerant passing holes formed therein and arranged longitudinally of the wall at a spacing, the heat exchange tubes of the front tube group having upper ends joined to the inlet header, the heat exchange tubes of the rear tube group having upper ends joined to the outlet header, the heat exchange tubes of the front tube group having lower ends joined to the inflow header, the heat exchange tubes of the rear tube group having lower ends joined to the outflow header. The refrigerant flowing into the inlet header of the inlet-outlet header tank flows through the heat exchange tubes of the front tube group into the inflow header of the turn header tank, then flows into the outflow header through the refrigerant passing holes in the partition wall and further flows into the outlet header of the inlet-outlet header tank through the heat exchange tubes of the rear tube group (see the publication of JP-A NO. 2003-75024).
However, the present inventor has conducted extensive research and consequently found that it is difficult to further improve the performance of the evaporator disclosed in the above publication for the reasons to be described below.
With the evaporator of the above publication, it is easier to give an increased cross sectional area to the channel inside the inlet header and reduced resistance to the channel than in the case of evaporators of stacked plate type. On the other hand, however, this increases the overall internal volume of the inlet header in which heat exchange tube ends are positioned. The evaporator is therefore likely to become slower in responsiveness to the turning on and off of the compressor. Stated more specifically, if the inlet header has an increased internal volume in its entirety, the rate of flow of the refrigerant is lower therein, and unless a certain amount of the refrigerant collects in the entire interior of the inlet header of increased internal volume which is in communication with the heat exchange tubes, the refrigerant will not flow into the heat exchange tubes. For these reasons, it will take some time for the evaporator to start to become cool when the compressor is turned on. Conversely when the compressor is turned off, the rise in the temperature of the evaporator will involve variations to result in variations in the temperature of the air to be discharged from the evaporator because of the increased overall internal volume of the inlet header and also because of variations in the amount of refrigerant remaining in the inlet header with respect to the direction of parallel arrangement of the heat exchange tubes. Further when the inlet header has an increased internal volume and if the flow rate of the refrigerant is low, the refrigerant flowing into the inlet header will not smoothly flow to a location remote from the refrigerant inlet. A large amount of refrigerant will then flow into the heat exchange tubes of the front tube group which are located closer to the inlet than the other tubes, while a small amount of refrigerant will flow into the tubes which are remote from the inlet to result in a reduced flow rate. Even in the case of heat exchange tubes of the rear group, a large amount of refrigerant will flow into the tubes positioned close to the inlet, whereas a lesser amount of refrigerant will flow into the tubes which are remote from the inlet. As a result, the amount of refrigerant contributing to heat exchange involves variations throughout the heat exchange core with respect to the lengthwise direction of the inlet header tank, and the air passing through the heat exchange core also varies in temperature at different locations. Thus, the evaporator fails to exhibit fully improved heat exchange performance.
An object of the present invention is to overcome the above problem and to provide a heat exchanger which is outstanding in heat exchange performance.